1. Field of the Invention
The present invention relates to a keyboard device for an electronic keyboard instrument, which is applied to an electronic keyboard instrument, such as an electronic piano, and has a let-off function of giving let-off feeling closely analogous to that of an acoustic piano.
2. Description of the Related Art
A general acoustic piano is constructed such that changes in the touch weight (static load) of each key during key depression, more specifically, a sharp increase in the touch weight and a sharp reduction in the same immediately after the increase, occur to add a so-called let-off feeling to a touch feeling felt by the player while playing the piano. The touch feeling of each key is important in playing the piano and particularly in achieving musical performance rich in expression. Therefore, in an electronic keyboard instrument, such as an electronic piano, it is preferable to obtain touch feeling similar to that of an acoustic piano. For this reason, keyboard devices having a let-off function of giving let-off feeling have been developed for various kinds of electronic keyboard instruments, and as such a keyboard device, there have conventionally been known ones disclosed e.g. in Japanese Patent Publications No. 3862858 and No. 3767153.
The keyboard device disclosed in Japanese Patent Publication No. 3862858 includes a plurality of keys arranged side by side in the left-right direction and each having a rear end thereof pivotally supported, a plurality of hammers provided below the respective keys in association therewith such that each of the hammers can pivotally move vertically in accordance with key depression and key release in one keystroke of an associated key, and let-off units each disposed behind an associated key and an associated hammer to add a let-off feeling to the touch feeling of the key. Each of the let-off units includes a jack projecting toward an associated hammer, a jack holder which pivotally supports the jack and is pivotally supported itself, and first and second elastic members for urging the jack and the jack holder, respectively, in respective predetermined directions.
In the keyboard device, when a key is depressed, an associated hammer pivotally moves upward in accordance with the key depression and comes into contact and engagement with an associated jack from below. In this case, the jack pivotally moves rearward against the urging force of the first elastic member in one piece with an associated jack holder. When the hammer further moves upward, the engagement with the jack is released. When the hammer is thus brought into temporary engagement with the jack during key depression, a load temporarily acts on the hammer in an opposite direction to a direction of the pivotal motion of the hammer, whereby the touch weight of the key is sharply increased and then sharply reduced. Thus, a let-off feeling is added to the touch feeling. When the key is released after the key depression, the hammer pivotally moves downward in accordance with the key release to return to its original position. In this case, the hammer comes into contact and engagement with the jack from above during the pivotal return motion. As a consequence, the jack pivotally moves downward against the urging force of the second elastic member, and the hammer further moves downward, whereby the engagement with the jack is released.
On the other hand, the keyboard device disclosed in Japanese Patent Publication No. 3767153 includes a plurality of keys and hammers similar to those in Japanese Patent Publication No. 3862858, and leaf springs each disposed reward of associated ones of these on a hammer-by-hammer basis to add a let-off feeling to the touch feeling of the key. The leaf spring extends horizontally in the front-rear direction and has a rear end thereof fixed to a mount having a predetermined shape. Specifically, the mount has first and second supports in contact with the respective upper and lower surfaces of the leaf spring, and the first support is formed at a predetermined location closer to the front end of the leaf spring as a free end thereof than the second support is.
In this keyboard device, when a key is depressed, an associated hammer pivotally moved upward in accordance with the key depression comes into contact and engagement with the front end of the leaf spring from below. In this case, the leaf spring is deflected upward using the first support as a support, and the hammer further pivotally moves upward, whereby the engagement with the leaf spring is released. When the hammer is thus brought into temporary engagement with the leaf spring during key depression, the touch weight of the key is sharply increased and then sharply reduced similarly to the keyboard device disclosed in Japanese Patent Publication No. 3862858, whereby a let-off feeling is added to the touch feeling. When the key is released after the key depression, the hammer pivotally moves downward in accordance with the key release to return to its original position. In this case, the hammer comes into contact and engagement with the front end of the leaf spring from above during the pivotal return motion. As a consequence, the leaf spring is deflected downward using the second support as a support differently from the case where the key is depressed, and the hammer further pivotally moves downward, whereby the engagement with the leaf spring is released.
In the keyboard device disclosed in Japanese Patent Publication No. 3862858, since the let-off unit for giving let-off feeling comprises the jack and the jack holder connected to each other in a pivotally movable manner, the first and second elastic members, and so forth as described hereinbefore, the total number of component parts is large, and the construction is complicated, which causes an increase in manufacturing costs of the keyboard device. On the other hand, in the keyboard device disclosed in Japanese Patent Publication No. 3767153, since the leaf spring is deflected upward and downward using the respective different supports by key depression and key release, long-term use can reduce the resilience of the leaf spring obtained by deflection or deform the leaf spring, depending on the material of the leaf spring. In such a case, there is a fear that it is impossible to obtain sufficient let-off feeling in appropriate timing during key depression.